问题 选择题

继首次载人航天飞行成功后,我国自行研制的“中星”20号通信卫星在西昌发射中心由“长征”二号运载火箭发射升空.用于发射火箭的燃料是偏二甲肼(用R表示),偏二甲肼与四氧化二氮剧烈反应,产生大量气体并释放出大量的热,该反应的化学方程式为:R+2N2O4═3N2+2CO2+4H2O,则R的化学式是(  )

A.C2H8N2

B.C2H8

C.C5H6O

D.C2H5N

答案

由反应的化学方程式R+2N2O4═3N2+2CO2+4H2O,可得知:

      反应前  反应后

N原子    4      6

O原子    8      8

C原子    0      2

H原子    0      8

根据化学变化前后原子的种类、数目不变,可判断每个反应物R的分子由2个C原子、8个H原子和2个N原子构成,则物质R的化学式为C2H8N2

故选A.

完形填空

Chinese scientists are again becoming excited about the fact that a large hairy animal may live in central China. Now they hope it won't be too long before they are able to __71 its existence. Their confidence is the __72 of a new discovery of the mystery animal in Hubei Province.

Ten Chinese __73 , enjoying a holiday in a National Forest Park, were driving down a road. As their bus turned a corner, the men were suddenly __74  by what they saw. Three __75 animals, covered with long dark hair, were crossing the road. On seeing the animals, the engineers immediately stopped and __76them. __77 ,when they saw how the animals moved through the forest with great __78 and strength, they did not dare to follow any further.

The men did not take any __79 . However, scientists are __80 by the discovery, because the engineers were all very educated people and scientists feel they can __81  what they described.

After the discovery, scientists returned to the forest and __82  some hair and measured footprints. About 20 inches appears to be the length of the animal's foot! Chinese scientists have now set up a special group to exchange information and make a __83 of the forest. But in the meantime,some people __84to believe that this halfman, halfmonkey exists. They will not believe that it is __85 until one of the animals has been caught.

71. A. prove         B. analyze         C. protect         D. check

72. A. basis         B. requirement     C. result          D. preparation

73. A. travellers    B. engineers       C. scientists      D. explorers

74. A. frightened    B. amazed          C. upset           D. inspired

75. A. trained       B. rejected        C. tall            D. violent

76. A. shot at       B. looked at       C. fought with     D. ran after

77. A. However       B. Indeed          C. Meanwhile       D. Anyway

78. A. difficulty    B. speed           C. care            D. pleasure

79. A. bullets       B. tools           C. medicines       D. photographs

80. A. surprised     B. delighted       C. disturbed       D. supported

81. A. rely on       B. deal with       C. write down      D. pass on

82. A. cut           B. pulled          C. collected       D. tore

83. A. film          B. tour            C. choice          D. study

84. A. come          B. refuse          C. prefer          D. have

85. A. wrong        B. alive           C. real            D.correct

单项选择题